The stress relaxation behavior of three NiCrAlY alloys that are common
ly used as bond coats for thermal barrier coatings (TBCs) has been dir
ectly measured. The relaxation study was conducted at temperatures of
800-1000-degrees-C and over a wide range of stresses. It was establish
ed that all three bond coat alloys relaxed quite rapidly at temperatur
es of 900-degrees-C and above. Since the upper use temperatures for bo
nd coats in gas turbine engines are between 900 and 1000-degrees-C, bo
nd coat relaxation is expected to occur in service. Therefore, relaxat
ion of the bond coat has the potential to affect TBC life. Furthermore
, the relaxation differences observed between the three alloys offers
a possible explanation for the differences in TBC life observed for th
ese bond coats. While bond coat relaxation is expected to occur for a
TBC in service, the mechanism for a relaxation effect on TBC life, if
it exists, is yet to be determined.